The U.S. Environmental Protection Agency's (EPA'S) water quality and hazardous wastes monitoring programs require quantitative analysis of a variety of environmental samples for volatile organic pollutant compounds. Determination of the volatile priority pollutants in water samples is usually satisfactorily accomplished by practicing EPA-recommended methods. However, the EPA-recommended precedures for the determination of volatile priority pollutants in soils, sediments and fish produce unacceptable results, as evidenced by low spike recoveries and high detection limits. Improved procedures have therefore been sought for effectively carrying out environmental monitoring programs with respect to solid samples of environmental matter.
The vaporization of volatile organic compounds from a sample under vacuum and the subsequent condensation of such compounds in a super-cooled trap seemed to offer some advantageous possibilities in such monitoring procedures since cryogenic concentration has been used successfully for the determination of tritiated methane and the radioisotopes of krypton and xenon. Accordingly, the use of cryogenic concentration appeared to be applicable for quantitatively determining the presence of volatile organic compounds in solid matrices. Vacuum extraction, moreover, was of advantage, in not requiring elevated temperatures or the addition of reagents which could produce unwanted contaminative byproducts due to sample degradation.
Having in mind the above factors, a particular method, known to the art as the purge-and-trap technique, for monitoring solid samples has been developed. In this method, volatile organic compounds are vaporized from the fish or soil sediment matrix under vacuum conditions and the vapors are condensed in a purging trap cooled by liquid nitrogen. The purging trap is transferred to a conventional purge and trap device where the concentrate is treated as a water sample and is analyzed by a Method 624 in the Federal Register 1979 (44FR 69532) developed by T. A. Bellar and J. J. Lichtenberg. Using this method of analysis, the average recovery of volatile organic compounds from samples spiked at the 25 mg/kg level was found to be 94% for sediments and 74% for fish tissue. An inherent problem encountered in the use of the purge-and-trap technique is that water vapor is carried along with the volatile organic compounds and this water interferes with the chromatographic analysis. Moreover, large amounts of carrier gas are needed to purge the volatile compounds. A jet separator or other carrier splitting device is then needed to remove most of the carrier gas. This results in the partial losses of the volatile compounds which limits sensitivity of the analysis.
In one modified purge-and-trap technique, developed by Joe Blazevich, a solid or biological sample is diluted with water and the resulting slurry is treated and analyzed as if it were an ordinary water sample. However, this process results in the foaming of the sample and in uncontrolled variable purging efficiencies.
Another modified purge-and-trap technique, developed by David Speis, uses steam distillation to separate the volatile compounds. The steal-carrier gas mixture is then passed through 5 ml. of water which serves as a conventional trap. However, the steam distillation may generate unwanted by-products due to the decomposition of labile components of the sample by heat, and some of the compounds of interest to the analysis may be lost due to chemical reaction or decomposition.
It is therefore evident from the above methods of analytically determining the volatile compounds in solid soil and biological environmental samples, certain disadvantages arise in reproducibly removing and concentrating the volatile organics for physicochemical determinations.
Since water has been routinely removed from molecular sieves using heat and vacuum and since it is known, as set forth above, that volatile compounds can be collected in a trap cooled with liquid nitrogen, it would appear that a combination of these techniques, with required modifications, could advantageously be used to remove and concentrate volatile organic compounds from a variety of matrices, such as the soil and biological samples, mentioned above.
Accordingly, the invention herein has been developed for the purpose of achieving the purposes set forth above without encountering the problems and disadvantages which have been described supra.